Reverse optical mastering for data storage disk replicas

ABSTRACT

A data storage master disk and method of making a data storage master disk. The data storage disk master is for use in a data storage disk replication process. The data storage disk molding processes produces replica disks having a surface relief pattern with replica lands and replica grooves. The method includes providing a master substrate. The master substrate is at least partially covered with a layer of photosensitive material. A surface relief pattern having master lands and master grooves is recorded in the data storage disk master, including the steps of exposing and developing the photosensitive material. The exposing and developing of a specified thickness of photosensitive material is controlled to form master grooves extending down to a substrate interface between the master substrate and the layer of photosensitive material, such that the width of the master grooves at the substrate interface corresponds to a desired width of the replica lands.

TECHNICAL FIELD

[0001] The present invention relates generally to the field ofmanufacture of optical data storage disks, and in particular, to anoptical disk mastering process for use in a disk molding process,capable of molding data storage disks containing a high density ofinformation.

BACKGROUND OF THE INVENTION

[0002] Optical disks are produced by making a master which has a desiredsurface relief pattern formed therein. The surface relief pattern iscreated using an exposure step (e.g., by laser recording) and asubsequent development step. The master is used to make a stamper, whichin turn is used to stamp out replicas in the form of optical mastersubstrates. As such, the surface relief pattern, information andprecision of a single master can be transferred into many inexpensivereplica optical disk substrates.

[0003] During the mastering exposure step, the mastering systemsynchronizes the translation position of a finely focused optical spotwith the rotation of the master substrate to describe a generallyconcentric or spiral pattern of a desired track spacing or “track pitch”on the disk. The generally spiral track forming the desired surfacerelief pattern as a result of the mastering process can be defined byhigh regions termed “lands” and lower adjacent regions termed “grooves”and/or pits (i.e., interrupted grooves). The recording power andsize/shape of the focused optical spot (spot size) as well as thephotosensitive material parameters determine the final geometry revealedin the master disk during the subsequent development step. Normalmastering practice uses high contrast positive photoresist for thephotosensitive material.

[0004] Conventional mastering typically utilizes laser light withwavelength, λ, in range of 350 nm<λ<460 nm focused through an objectivewith a numerical aperture (NA) of 0.75 nm<NA<0.90 to give a theoreticalgaussian spot size of:

[0005] SS=0.57λNA (full width at half maximum intensity (FWHM)). Thus, a350 nm laser light with NA=0.9 gives a theoretical spot size 0.22microns (FWHM) as the practical limit for conventional optics.

[0006] After the master is recorded, it is flooded with developersolution to reveal the exposure pattern applied by the master recordingsystem. The dissolution of the photoresist in the developer solution isin proportion to the optical exposure previously received in therecording process. The dissolution rate of the photoresist can bemodeled for given exposure and development conditions (see Trefonus, P.,Daniels, B., “New Principal For Imaging Enhancement In Single LayerPositive Photoresist”, Proc. of SPIE vol. 771 p.194 (1987), see alsoDill F. et al., “Characterization of Positive Photoresists” IEEETransactions on Electronic Devices, vol. ED-22 p. 445 (1975).)Expressions explained in these referenced technical papers can be usedto model the effects of exposures from several adjacent tracks recordedin the photoresist and subsequently developed. The photoresistdissolution in the developer solution is in proportion to the opticalexposure previously received (positive type resist). More accurately,the dissolution rate (R) is given by the Trefonas model as

R[nm/sec]=R ₀×(1−M)^(q) +R _(b)

[0007] Where R₀ and R_(b) are the dissolution rates of the fully exposedand unexposed photoresist (respectively), q is a resist parameterrelated to the resist contrast and M is the fractional unconvertedphotoactive compound in the resist. Typical values for commerciallyavailable resists are q=3, 10<R₀<200 [nm/sec] and R_(b)=0 for normaldeveloper concentrations. The M term is dependent in a point-wisefashion on how much exposure was received in the resist (E(x,y,z)) andthe resist's parametric sensitivity “C” per the Dill convention:

M(x,y,z)=exp{−C×E(x,y,z)}.

[0008] Since optical disk mastering typically uses only 50-200 nm ofphotoresist thickness, the z-dependence of exposure can safely beignored so that the above equations can be combined to give

R=R ₀(1−exp{−CE(x,y,)})^(q);

[0009] or, with the exposure profile explicitly circular gaussian we maysimplify to

R=R ₀(1−exp {−CkP exp [−r ² /SS ²]})^(q);

[0010] Where r measures the radial distance from the center of the spot(r²=x²+y²), P is the recording power and k is a normalization constantfor the guassian function. This dissolution rate, multiplied by thedevelopment time (t_(d)), gives the depth of photoresist lost from itsinitial coating thickness (T₀), so that the final resist thickness(T(t)) is given by T(td)=T₀−t_(d) R₀ (1−exp{−CkP exp[−r²/SS²]})^(q);From this expression one can see how optical exposure (P), development(t_(d), R₀) and photoresist thickness (T₀) determines final surfacerelief pattern.

[0011] In some aspects, these expose/development processes may becompared with conventional photography. In photography, either exposureor development may be controlled/adjusted as necessary to obtain desiredfinal development pattern. In this sense, one may consider theexpose/development level as one process variable which may alternativelybe controlled by recording power, development time, developerconcentration, etc.

[0012] In the mastering process, it is desirable to simultaneouslyobtain wide lands (for user recorded features) and grooves of suitabledepth for adequate tracking signals (e.g., greater than 50 nm). Higherdensity data storage disks often require the storage of a greater amountof information within the same or smaller size of disk area, resultingin smaller track pitch (i.e., distance between tracks) design criteria.

[0013] Attempts have been made to meet these design criteria. In priorart FIGS. 1-3, surface relief patterns of exemplary master disks formedusing conventional disk mastering techniques are illustrated using theabove expressions to model the effects of exposures from severaladjacent tracks recorded in the photoresist layer and then developed.These comparisons assume (1) typical photoresist and developerparameters, (2) constant development time (=40 sec.), (3) SS=0.23microns, (4) track pitch of 0.375 microns and initial photoresistthickness of 100 nm. As recording power (or alternatively, developmenttime) is increased to obtain deeper grooves, the residual land widthdiminishes and lands become more rounded due to overlap exposure fromadjacent tracks. Partially developed photosensitive material exhibits agranular roughness greater than that of the photosensitive material asinitially coated on the disk. Roughness of lands worsens with deepeningof grooves, resulting in additional noise in data readback.

[0014] More problems occur when the track pitch approaches the finitesize of the mastering spot size. For formats where the desired trackpitch is much larger (>2×) than the finite size of the mastering spotsize (ss), the photosensitive material erosion of the lands isnegligible and conventional mastering can provide wide lands with a >50nm groove depth. However, for formats where the track pitch is <2×larger than the spot size, conventional mastering requires a compromiseof either land width, groove depth, or both (due to overlap exposurefrom adjacent tracks).

[0015] In FIG. 4, exemplary embodiments of the mandatory link betweenland width and groove depth when using conventional mastering processesis illustrated. (Examples of 0.375 micron and 0.425 micron track pitchwith 0.22 micron recording spot size). As the groove depth increases,the land width decreases. The master surface relief pattern geometries(i.e, land width/groove depth) are constrained for given conditions oftrack pitch and mastering spot size. This means the designer may notindependently specify the desired parameters for replica land width andreplica groove depth.

[0016] A secondary problem for conventional mastering is that the landwidth precision is limited by mechanical track pitch precision (e.g.,mechanical precision of master recording system), which is increasinglydifficult to control as track pitch decreases.

SUMMARY OF THE INVENTION

[0017] The present invention provides a data storage master disk andmethod of making a data storage master disk wherein the user mayindependently specify the parameters of replica land width and replicagroove depth. The data storage master disk is for use in a data storagedisk molding process for producing replica disks which are capable ofstoring a high capacity of information using a variety of disk formats.

[0018] In a first embodiment, the present invention provides a method ofmaking a data storage master disk for use in a data storage disk moldingprocess. The data storage disk molding process produces replica diskshaving a surface relief pattern with replica lands and replica grooves.The method includes the step of providing a master substrate. The mastersubstrate is covered with a layer of photosenstive material having aspecified thickness. A surface relief pattern having master lands andmaster grooves is recorded in the data storage master disk, includingthe steps of exposing and developing the photosensitive material. Theexposing and developing of a specified thickness of a photosensitivematerial is controlled to form master grooves extending down to asubstrate interface between the master substrate and the layer ofphotosensitive material, such that the width of the master grooves atthe substrate interface corresponds to a desired width of the replicalands.

[0019] The thickness of the photosensitive material is specified andcontrolled to correspond to a desired depth of the replica grooves. Inanother aspect, the thickness of the photosensitive material isspecified and controlled in dependence on master recording system spotsize, desired track pitch, and desired depth of replica grooves. Thestep of controlling the exposure and development of the data storagemaster disk may include the step of controlling the exposing anddeveloping of the photosensitive material to obtain a flat master groovebottom. In another aspect, the step of controlling the exposure anddevelopment of the data storage master disk includes the step ofcontrolling the exposing and developing of the photosensitive materialto obtain a smooth, flat master groove bottom, with smoothnessdetermined by the master substrate.

[0020] The step of controlling the exposing and developing of thephotosensitive material may include the step of controlling opticalenergy for exposing the photosensitive material to a degree sufficientto obtain a desired master groove bottom width after development andremoval of the photosensitive material. In another aspect, the step ofcontrolling the exposing and developing of the photosensitive materialmay include the step of controlling the development of thephotosensitive material to a degree sufficient to obtain a desiredmaster groove width after development and removal of the exposedphotosensitive material.

[0021] The step of exposing and developing the data storage master diskmay include the step of forming a groove bottom, wherein the groovebottom is flat relative to the master land. The step of exposing anddeveloping the data storage master disk results in the data storagemaster disk having a master surface relief pattern defined by the masterlands and the master grooves, wherein the surface relief pattern of thereplica disks has an orientation which is inverse the orientation of thedata storage master disk surface relief pattern.

[0022] The present invention may further provide the step of polishingthe master substrate optically smooth; and forming a smooth mastergroove bottom using the master substrate. In one aspect, the step ofproviding a master substrate includes forming a master substrate made ofglass. Preferably, the glass is polished. The photosensitive materialmay be bonded to the master substrate with or without intermediatelayers.

[0023] The present invention may further provide for forming a firststamper using the data storage master disk. Replica disks are made usingthe first stamper. The step of making replica disks using the datastorage master disk may be accomplished using a multiple generationstamper process.

[0024] In another embodiment, the present invention provides a method ofmaking a replica disk from a master disk using an inverse stampingprocess. The replica disk is capable of storing high volumes ofinformation. The replica disk includes a surface relief pattern withreplica lands and replica grooves. The method includes the step ofproviding a master substrate. At least a portion of the master substrateis coated with a layer of photosensitive material to form the masterdisk. A surface relief pattern having master lands and master grooves isrecorded in the master disk, including the steps of using a laser beamrecorder for exposing the photosensitive material in a desired trackpattern having a track pitch, and developing the photosensitivematerial. The exposing and developing of the photosensitive material iscontrolled for forming master grooves extending down to a substrateinterface between the master substrate and the photosensitive material,such that the width of the master grooves at the substrate interfacecorresponds to a desired width of the replica lands. A first stamper isformed from the master disk. A second stamper is formed from the firststamper. A replica disk is formed from the second stamper, the replicadisk including a surface relief pattern having an orientation which isthe inverse of the master disk.

[0025] The present invention may further provide the step of controllingthe thickness of the layer of the photosensitive material to correspondto a desired depth of the replica grooves. The specified and controlledthickness of the photosensitive material depends on master recordingsystem spot size, desired track pitch, and desired depth of replicagrooves.

[0026] The step of controlling the exposing and developing of thephotosensitive material may include the step of controlling the exposingand developing of the photosensitive material to obtain a flat mastergroove bottom. Recording a desired track pitch in the photosensitivematerial may further include the use of a focused laser beam at a spotsize which is greater than one half of the track pitch.

[0027] The step of a master substrate may include providing a mastersubstrate made of glass. Further, the master substrate may be polished.

[0028] In one aspect, the desired track pattern is a spiral trackdefined by adjacent master lands and master grooves, wherein the stepsof exposing/developing the master disks includes forming a wide, flatmaster groove bottom defined by the disk substrate. The step ofrecording the master disk includes forming master groove bottoms havinga width which does not necessarily depend on the depth of the mastergroove for a desired track pitch. The resulting depth of the mastergroove is dependent on the specified thickness of the photosensitivematerial and the cumulative optical exposure received by thephotosensitive layer at a position half way between two adjacent tracks.In particular, this depends on the desired groove bottom width and theratio of master recording spot size to desired track pitch.

[0029] In another embodiment, the present invention provides a masterdisk. The master disk includes a master substrate. A layer ofphotosensitive material covers at least a portion of the mastersubstrate. The photosensitive material includes a surface relief patternin the form of a track pattern defined by adjacent master lands andmaster grooves. The master grooves extend down to the disk substrate,the master grooves including a master groove bottom and the master landsincluding a master land top, wherein the master groove bottom is widerthan the master land top.

[0030] The master groove bottom is generally flat. In particular, themaster groove bottom is flat relative to the master land top, and inparticular, the master groove bottoms may be wide and flat relative tothe master land tops. Preferably, the master groove bottoms includesharp corners. Additionally, all of the master groove bottoms on theexposed/developed master disk are level with each other to the precisionof the master substrate flatness. This is important in flying head mediaapplications, such as near field recording techniques, where smalllenses fly in proximity to the replica disk surface.

[0031] The master grooves may include a groove depth which is proximatethe thickness of the photosensitive material for cases where the trackpitch is greater than approximately 1.6 times the spot size. In oneaspect, the master grooves include a groove depth which is greater than50 nanometers, track pitch is less than two times the mastering systemspot size, and the width of the master groove bottom is greater than 25percent of desired track pitch. In another aspect, the width of themaster groove bottom is greater than 50 percent desired track pitch.

[0032] In another embodiment, the present invention provides a diskincluding a replica substrate having a first major surface and a secondsurface. The first major surface includes a surface relief pattern inthe form of a track pattern defined by adjacent lands and grooves. Thetrack pattern having a track pitch less 0.425 nanometers, wherein thegrooves extend down into the disk substrate. The grooves include agroove bottom and the replica lands include a land top, wherein the landtop is flat. This is particularly important in near field recordingtechniques, wherein lens-to-media-surface separation is extremelycritical.

[0033] In one aspect, the land top has a width greater than 25 percentof track pitch. In one preferred aspect for the track pitch less than orequal to 400 nanometers, the groove depth is greater than 80 nanometersand the land width is greater than 160 nanometers. Preferably, the landtop is smooth and has sharp edges. In one preferred embodiment, the landtops are level with each other to the precision of the flatness of themaster disk substrate. The land tops are level and at the same elevationrelative to the second major surface. This is important in flying headmedia applications, such as near field recording techniques, where smalllenses fly in proximity to the replica disk surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings are included to provide a furtherunderstanding of the present invention and are incorporated in andconstitute a part of this specification. The drawings illustrate theembodiments of the present invention and together with the descriptionserve to explain the principals of the invention. Other embodiments ofthe present invention and many of the intended advantages of the presentinvention will be readily appreciated as the same become betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, in which likereference numerals designate like parts throughout the figures thereof,and wherein:

[0035]FIG. 1 is a partial cross section illustrating the surface reliefpattern of a prior art recorded master disk;

[0036]FIG. 2 is a partial cross-section illustrating the surface reliefpattern of another master disk made using a prior art recording process;

[0037]FIG. 3 is a partial cross-section illustrating the surface reliefpattern of another master disk made using a prior art recording process;

[0038]FIG. 4 is a graph illustrating master groove depth versus masterland width for a master disk made using prior art mastering/recordingtechniques;

[0039]FIG. 5 is a plan view illustrating one exemplary embodiment of arecorded master disk made using a data storage disk mastering process inaccordance with the present invention;

[0040]FIG. 6 is an enlarged partial cross-sectional view taken alongline 6-6 of FIG. 5;

[0041]FIG. 7 is an enlarged partial cross-sectional view illustrating astep in making a master disk in accordance with the present invention;

[0042]FIG. 8 is a diagram illustrating another step in making a masterdisk in accordance with the present invention;

[0043]FIG. 9 is a diagram illustrating one exemplary embodiment of thesurface geometry of a master disk made using the process in accordancewith the present invention;

[0044]FIG. 10 is a diagram illustrating another exemplary embodiment ofthe surface geometry of a master disk made using the process inaccordance with the present invention;

[0045]FIG. 11 is a diagram illustrating another exemplary embodiment ofthe surface geometry of a master disk made using the process inaccordance with the present invention;

[0046]FIG. 12 is a graph illustrating maximal master groove depth versusmaster groove bottom width for examples of master disks made using themastering process in accordance with the present invention;

[0047]FIGS. 13-18 illustrate experimental atomic force microscope tracesof several differing surface relief geometries for master disks recordedat 0.375 and 0.425 micron track pitch using the mastering process inaccordance with the present invention;

[0048]FIG. 19 is a diagram illustrating groove orientation for replicadisks made from a master disk in accordance with the present invention,using a multiple generation disk molding/replication process;

[0049]FIG. 20 is a block diagram illustrating a data storage diskmastering process in accordance with the present invention; and

[0050]FIG. 21 is a block diagram illustrating a process for making areplica disk using a master disk in accordance with the presentinvention.

DETAILED DESCRIPTION

[0051] The present invention includes a data storage master disk andoptical disk mastering process for making the unique data storage masterdisk. The process in accordance with the present invention provides fora master data storage disk having grooves which extend down to themaster substrate, resulting in deep, flat, and wide master disk grooves.The master disk can be used in a disk molding process which includes areverse mastering/inverse stamping process, resulting in replica diskshaving wide, flat lands with sharp edges, and deep grooves relative toreplica disks formed using conventional mastering processes. As such,the present invention is particularly useful in enabling flexible designof surface relief geometry for molded data storage disks containing ahigh density of information. This includes the ability to create wide,flat land features even in replica disks having a track pitch of lessthan two times the mastering system laser beam spot size.

[0052] In FIG. 5, a data storage master disk 20 in accordance with thepresent invention is generally shown. Master disk 20 may be used as partof a disk replication process (e.g., a disk molding process) forproducing various formats of optical data disks. The data features onthe optical data disks may include data pits, grooves, bumps or ridges,and land or land areas. This includes current formats of audio CD,CD-ROM and video disk, such as DVD, as well as future formats which usedata features described herein. The definition of optical data disks mayinclude various types of recordable optical disks (e.g., CDR,magneto-optic, or phase-change disk formats, which commonly usefeatures, such as grooves or pits, for tracking and addressidentification, even though data is subsequently recorded by the users.

[0053] Master disk 20 includes a surface relief pattern (i.e., surfacegeometry) in the form of “data tracks” 22 (shown enlarged for clarity)which may include features representing data encoded therein or whichallow the storage, reading, and tracking of data thereon. Data tracks 22on the optical disk can be arranged in a spiral track 24 originating atthe disk center 26 and ending at the disk outer edge 28, oralternatively, the spiral track 24 may originate at the disk outer edge28 and end at the disk center 26. The data can also lie in a series ofconcentric tracks spaced radially from the disk center 26. Master disk20 may or may not include a center hole, and may be hubbed or hubless.

[0054] In FIG. 6, a partial cross-sectional view illustrating oneexemplary embodiment of master disk 20 in accordance with the presentinvention is shown. Master disk 20 includes data layer 30 and mastersubstrate 32 (a portion of which is shown). The data layer 30 includes asurface relief pattern shown as data tracks 22. The data tracks 22 aredefined by a series of adjacent master lands 34 and master grooves 36formed in the data layer 30 (e.g., which form spiral track 24). Themaster groove sides 38, 40 are defined by adjacent master lands 34, andinclude a master groove bottom 42 which is defined by the mastersubstrate 32. Master substrate 32 provides for a wide, flat and smoothmaster groove bottom 42.

[0055] Data layer 30 is made of a photosensitive material, and morepreferably, is made of a photopolymer or photoresist. Master grooves 36have a depth 44 which is equal to the height of master lands 34 relativeto master substrate 32, and related to the initial thickness of datalayer 30. Master groove depth 44 may further be dependent on masteringspot size, track pitch, and photoresist contrast. Preferably, mastergrooves 36 have a depth greater than 50 nm, and which typically rangesbetween 50 nm and 120 nm. Master groove bottom 42 is preferably flat andsmooth as defined by master substrate 32, having a width 46 which ispreferably greater than 35 percent of the desired track pitch.

[0056] In one preferred embodiment, master substrate 32 is made ofglass, and is preferably polished and/or optically smooth. The mastersubstrate 32 typically varies in thickness between 5 mm and 6 mm. Datalayer 30 can be bonded to master substrate 32. In particular, data layer30 may be coated directly to master substrate 32 or may include anintermediate layer (which may be a bonding layer).

[0057] The disk mastering process in accordance with the presentinvention provides for master disk 20 having relatively deep mastergrooves 36 with wide, flat master groove bottoms 42. As such, whenmaster disk 20 is used in a reverse optical disk mastering process, themaster lands and master grooves translate into a replica disk havingrelatively deep grooves and wide flat lands. Such characteristics arepreferred for many high density and writeable optical disk formats.

[0058] The master groove bottoms defined by the disk mastering processin accordance with the present invention are flat (as opposed to roundedin the conventional process) with smoothness defined by the mastersubstrate (e.g., polished glass) and includes sharp corners. When usedin connection with an inverse stamping process, this corresponds toreplica disks having wide, flat smooth lands with sharp corners, anddeep grooves. Wide, flat lands are advantageous for positioning userrecorded data thereon. The sharp corners provide domain confinement foruser recorded data (e.g., applications wherein data is magneto-opticallyrecorded on the tops of lands). The wide, flat lands with sharp cornersand deep grooves provide for improved tracking or trackability of themedia substrate. The replica disk land tops are very smooth, due to thegroove bottoms 42 which are defined by the master substrate 32, which ispreferably optically polished glass. The smoothness of the land tops isdefined by the substrate interface between the master substrate 32 andthe layer of photosensitive material 30. Smoothness of land tops resultsin a reduction of noise in subsequent readout of data from the disk.

[0059] Further, the wide, flat lands are level with each other, due tothe groove bottoms 42 being defined by the master substrate 32. The flatlands are level with each other and at the same elevation, enhancing theflyability of the disk substrate for flying head applications.

[0060] Referring to FIGS. 7 and 8, a method of making an optical diskmaster for use in a data storage disk molding process, in accordancewith the present invention, is illustrated. In FIG. 7, master substrate32 is provided which is preferably made of glass. Master substrate 32typically ranges in thickness between 5 mm and 6 mm. Master substrate 32includes major surface 50. Preferably, major surface 50 is polishedoptically smooth. Major surface 50 is at least partially covered (e.g.,coated) by data layer 30. Data layer 30 may also be coated over anintermediate (e.g., bonding) layer 60 (not shown).

[0061] Referring to FIG. 8, master disk 20 is positioned on a masterrecording system (e.g. a laser recorder or a mask recording system). Inone exemplary embodiment, the master recording system 60 includescontroller 61, linear translation system 62, master recorder 64 andrecording table 66. Master recording system 60 provides for controlledexposure of master disk 20 with a focused spot of laser light to encodethe desired surface relief pattern (i.e., geometry) or data trackstherein.

[0062] Master disk 20 is placed on recording table 66, and can beregistered (e.g., centered) about a center axis 68, relative to masterrecorder 64 using techniques as known in the art, such as through theuse of a spindle, or hubbed master disk 20. Recording table 66 isrotatable about the center axis 68, indicated by rotation arrow 70, forrotation of master disk 20 during the disk recording process. Masterrecorder 64 modulates and focuses a laser beam 72 for exposure of datalayer 30 in a desired pattern. Further, master recorder 64 ismechanically coupled to linear translation system 62 which provides foraxial movement of master recorder 64 relative to center axis 68,indicated by directional arrow 76.

[0063] Controller 61 is coupled to linear translation system 62 andmaster recorder 64 (indicated at 61A) and is coupled to recording table66 (indicated at 61B). The controller 61 operates to synchronize thetranslation position of the finally focused laser beam 72 with therotation 70 of master disk 20 to expose spiral track 24 in data layer30. Further, controller 61 may operate to modulate laser beam 72 toexpose pit regions (interrupted grooves) in the header area of the disk.Controller 61 can be a microprocessor based programmable logiccontroller, a computer, a sequence of logic gates, or other device whichmay be capable of performing a sequence of logical operations.

[0064] In accordance with the present invention, controller 61 operatesto control the optical energy of master recording system 60 for exposingthe photosensitive material of master disk 20 to a degree sufficient toobtain a desired master groove bottom width after development andremoval of the exposed photosensitive material. Controlling the opticalenergy can include controlling either the recording power or controllingthe recording speed for exposing the photosensitive material to a degreesufficient to obtain a desired master groove bottom width afterdevelopment and removal of the exposed photosensitive material. Forexample, controller 61 may operate to increase the recording power ordecrease the recording speed, thereby increasing optical exposure of thephotosensitive material.

[0065] The laser recorded master disk 20 is removed from the recordingtable 66 and flooded with a developer solution to reveal the exposurepattern provided by the master recording system 60. The amount ofdissolution of the data layer 30 in the developer solution is inproportion to the optical energy previously received during therecording process. Further, the amount of dissolution of the data layer30 in the developer solution is in proportion to development processparameters, including the concentration of the development solution, thedevelopment time and temperature. The type of development solution canbe similar to development solutions used in conventional recordingprocesses as known to those skilled in the art. As such, by controllingthe exposure and development processes, the desired surface reliefpattern in the photosensitive material can be achieved. Since the masterrecording system 60 was controlled to fully dissolve portions of thedata layer 30 down to the master substrate 32, the resulting mastergrooves (previously shown in FIG. 6) include master groove bottoms whichare defined by the master substrate 32 and, in particular, for recordedtrack pitches of less than 2 times the mastering spot size. The abovemaster disk process results in master lands having rounded peaks andmaster grooves having flat, wide and preferably smooth master groovebottoms.

[0066] In FIGS. 9-11, exemplary embodiments are shown illustrating thesurface relief pattern or data tracks for master disks 20A, 20B, 20Cwhich have been “overexposed” or “overdeveloped” using the masterrecording process in accordance with the present invention. With eachfigure (i.e., FIGS. 9-1l ), the amount of exposure/development of datalayer 30 has been increased. Referring to FIG. 9, the masterrecording/developing process resulted in master lands 34A definingmaster grooves 36A exposed down to master substrate 32A. Master grooves36A have a groove depth of 92 nm with a corresponding flat master groovebottom 42 having a width of 120 nm. Similarly, FIG. 10 illustratessurface relief pattern or data tracks 22B having master lands 34B whichdefine master grooves 36B down to master substrate 32B. The mastergrooves 36B have a groove depth of 88 nm and a corresponding flat mastergroove bottom 42 which is 160 nm wide. FIG. 11 illustrates master disk20C having master lands 34C which define master grooves 36C havingmaster groove bottom 42C defined by master substrate 32C. Master groove36C has a groove depth of 82 nm and a flat master groove bottom 42 whichis 200 nm wide. The more master disk 20 is overexposed during diskrecording process, the greater the erosion of the master lands and widermaster groove bottoms are achieved.

[0067] In FIG. 12, a graph illustrating the corresponding relationshipbetween master land width and master groove depth using the masterrecording process in accordance with the present invention is shown.Using conventional mastering processes, for a given data layerthickness, master groove depth and master groove bottom width are linkedand dependent upon each other (see FIG. 4). Using the mastering processin accordance with the present invention, by selection of the initialthickness of the data layer and expose/development level, one canindependently specify land width and groove depth. In other words,master groove depth is not dependent upon master groove bottom width,and master groove bottom width is not dependent upon master groovedepth. The two parameters are separable, and by selecting a desired datalayer thickness, and controlling exposure and development criteria, adesired design criteria for the master disk may be obtained.

[0068] In the exemplary embodiment shown, plots are shown illustratingdesign criteria achieved by increasing initial photosensitive (data)layer thickness (plot 78) and/or increasing exposure energy/developmentof the photosensitive layer (plot 79). In all examples, a 0.22 micronspot size is assumed. Plot 80 had an initial data layer thickness of 120nm, plot 82 had an initial data layer thickness of 100 nm, plot 84 hadan initial data layer thickness of 80 nm, and plot 86 had an initialdata layer thickness of 60 nm. As illustrated, master surface geometriesare no longer constrained by the master land width to master groovedepth linkage as in conventional mastering processes. By starting withdifferent initial data layer thicknesses and controlling exposedevelopment level, any point within the width-depth parameter space maybe obtained using the disk mastering process in accordance with thepresent invention. Whereas FIG. 12 shows how by starting with differinginitial photosensitive material thickness that any point in thewidth-depth parameter space may be obtained, FIGS. 13-18 showcorroborating experimental results illustrated by atomic forcemicroscope (AFM) traces of several differing geometries at 0.375 and0.425 micron track pitch using the disk mastering process in accordancewith the present invention.

[0069] The master recording process in accordance with the presentinvention is (preferably) used in a reverse mastering or inversestamping process, for creation of replica disks having wide, flat (andsmooth) land features at track pitches less than two times the masteringsystem spot size. In FIG. 19, a diagram illustrating “groove”orientation of an optical disk substrate (i.e., a replica disk) moldedfrom a first generation stamper, a second generation stamper or a thirdgeneration stamper formed from a master disk in accordance with thepresent invention, is shown. The diagram includes enlarged, partialcross-sections illustrating the orientation of the data tracks of amaster disk 90, first generation stamper 92, second generation stamper94, third generation stamper 96, replica disk substrate 1, replica disksubstrate 2, and replica disk substrate 3. Data tracks are recorded ontothe master disk 90, and have an orientation based on whether a replicadisk substrate is molded from a first, second or third generationstamper.

[0070] In particular, master disk 90 includes master data layer 104having master lands 106 and master grooves 108. First generation stamper92 includes first generation stamper data layer 110 having firstgeneration stamper lands 112 and first generation stamper grooves 114.Second generation stamper 94 includes second generation stamper datalayer 116 having second generation stamper lands 118 and secondgeneration stamper grooves 120. Third generation stamper 96 includesthird generation stamper data layer 122 having third generation stamperlands 124 and third generation stamper pits 126. Similarly, replica disksubstrate 1 includes substrate 1 data layer 128 having substrate 1 lands130 and substrate 1 grooves 132; replica disk substrate 2 includessubstrate 2 data layer 134 having substrate 2 lands 136 and substrate 2grooves 138; and replica disk substrate 3 includes substrate 3 datalayer 140 having substrate 3 lands 142 and substrate grooves 144.

[0071] The orientation of substrate 1, data layer 128 molded from firstgeneration stamper 92 corresponds to the orientation of the master diskdata layer 104. In particular, the first generation stamper data layer110 is the inverse of the master disk layer 104. Similarly, replica disksubstrate 1 data layer 128 is the inverse of the first generationstamper data layer 110.

[0072] Second generation stamper 94 data layer 116 is the inverse of thefirst generation stamper 92 data layer 110, resulting in replica disksubstrate 2 data layer 134 being the inverse of second generationstamper 94 data layer 116 and master disk data layer 104. Likewise,third generation stamper 96 data layer 122 is the inverse of the secondgeneration stamper 94 data layer 116. Accordingly, disk substrate 3,data layer 140 is the inverse of the third generation stamper data layer122, and corresponds or has the same orientation as the master disk datalayer 104.

[0073] It is recognized that the desired orientation of the master diskdata layer 104 is dependent on the desired orientation of the replicadisk substrate for its intended use. For the example of high-densityreplica disks having track pitches less than two times the masteringsystem spot size (and air incident media), it is desirable to use amaster disk form using the master disk recording process in accordancewith the present invention and a second generation stamper process,resulting in a replica disk having wide, flat, smooth lands and deepgrooves. Alternatively, for disks read through the substrate, a masterdisk formed using the master disk recording process in accordance withthe present invention may be used in a first generation stamper or thirdgeneration stamper process where it is desired to mold a replica diskhaving flat pits or grooves.

[0074] In one preferred embodiment, a master disk made using the masterdisk recording precess in accordance with the present invention isutilized in a second generation disk molding process. Suitable diskmolding processes including one suitable second generation disk moldingprocess capable of making multiple optical disk stampers from one masterdisk is as disclosed in U.S. patent application Ser. No. ______, filed______ titled “PROCESS FOR MAKING MULTIPLE DATA STORAGE DISK STAMPERSFROM ONE MASTER” (Kerfeld) (Attorney Docket No. I201\106.101), filed thesame date as the instant application, the disclosure of which isincorporated herein by reference. The above-referenced patentapplication utilizes a unique disk molding process which includes aphotopolymerization step which is non-destructive to either the recordedmaster, first generation stamper or second generation stamper. Thisallows many next generations stampers to be made, while maintaining theintegrity of the data layer transferred from the previous generationdisk. In one embodiment, a portion of a first stamper which defines thedata layer is transferred to and becomes part of a second stamperwithout changing the integrity of the data layer.

[0075] Alternatively, other stamper processes may be utilized. Forexample, in another exemplary embodiment an electroforming pyramidingfamily process is used. This process involves the electroforming of a“father” stamper or first generation stamper from a master disk formedusing the process in accordance with the present invention. The fatherstamper is cleaned, treated and returned to the nickel bath to plate a“mother” or second generation stamper. This process cycle can berepeated several times, resulting in multiple “mother” stampers orsecond generation stamper being made from a single father or firstgeneration stamper. The same electroforming process may be repeatedusing the “mother” stamper to make several “daughter” or thirdgeneration stampers from each mother.

[0076] In FIG. 20, a block diagram illustrating a process for making areplica disk using a master disk made in accordance with the presentinvention is shown at 110. The master disk is for use in a data storagedisk molding process. The data storage disk molding process producesreplica disks having a surface relief pattern with replica lands andreplica grooves. In the exemplary embodiment shown, the process 110begins with providing a master substrate (112). The master substrate isat least partially covered with a photosensitive material, which ispreferably made of photoresist (114). A surface relief pattern havingmaster lands and master grooves is recorded in the data storage masterdisk, including the steps of exposing and developing the photosensitivematerial (116). The exposing and developing of a specified thickness ofphotosensitive material is controlled to form master grooves extendingdown to substrate interface between the master substrate and the layerof photosensitive material, such that the width of the master grooves atthe substrate interface corresponds to a desired width of the replicalands (118).

[0077] The master disk can now be used to make a replica disk in a diskmolding process. In particular, a stamper is made from the opticalmaster disk (120). A replica disk is made from the stamper (122). Thereplica disk is capable of storing high volumes of information. In oneapplication, this invention is particularly useful for recording trackpitches that are less than 2 times the master recorder spot size.

[0078] In FIG. 21, a block diagram illustrating one exemplary embodimentof using a master disk in accordance with the present invention in amultiple generation disk molding process is shown at 130. The masterdisk is fabricated (132) using the unique methods previously describedherein. The methods include exposing and developing the data layer downto the master substrate. A first generation stamper is made from themaster disk (134). A replica disk may be made from the first generationstamper (136).

[0079] Alternatively, a second generation stamper is made from the firstgeneration stamper (138). A replica disk is made from the secondgeneration stamper (140). Further, a third generation stamper can bemade from the second generation stamper (142). A replica disk can bemade from the third generation stamper (144).

[0080] Photosensitive materials include photopolymers or photoresist, orother materials or material blends having similar photosensitivecharacteristics. One group of suitable photosensitive material includesstandard position type high resolution photoresist commerciallyavailable from vendors Shipley, OCG, etc. Other suitable photosensitivematerials may become apparent to those skilled in the art afterreviewing this disclosure.

[0081] Suitable photopolymers for use in forming layers, replicationlayers, or bonding layers discussed herein, include HDDA (4×6×)polyethylenically unsaturated monomer-hexanediol diacrylate; chemlink102 (3×) monoethylenically unsaturated monomer-diethylene glycolmonoethyl ether acrylate, elvacite 2043 (1×3×) organicpolymer-polyethylmethacrylate, and irgacure 651 (0.1×0.2) latent radicalinitiator-2,2-dimethoxy-2-phenylacetophenone. Another suitablephotopolymer includes HHA (hydantoin hexacryulate) 1×, HDDA (hexanedioldiacrylate) 1×, and irgacure 651 (0.1×0.2) latent radicalinitiator-2,2-dimethyoxy-2phenylacetophenone. Other suitablephotopolymers may become apparent to those skilled in the art afterreviewing this disclosure.

[0082] Numerous characteristics and advantages of the invention havebeen set forth in the foregoing description. It will be understood, ofcourse, that this disclosure is, and in many respects, onlyillustrative. Changes can be made in details, particularly in matters ofshape, size and arrangement of parts without exceeding the scope of theinvention. The invention scope is defined in the language in which theappended claims are expressed.

What is claimed is:
 1. A master disk comprising: a master substrate; alayer of photosensitive material covering at least a portion of themaster substrate, the photosensitive material including a surface reliefpattern in the form of a track pattern defined by adjacent master landsand master grooves, wherein the master grooves extend down to the mastersubstrate, the master grooves including a master groove bottom and themaster lands including a master land top, wherein the master groovebottom is wider than the master land top.
 2. The master disk of claim 1,wherein the master groove bottom is generally flat.
 3. The master diskof claim 1, wherein the master groove bottoms are flat relative to themaster land tops.
 4. The master disk of claim 1, wherein the mastergroove bottoms are level with each other.
 5. The master disk of claim 1,wherein the master groove bottoms are wide and flat relative to themaster land tops.
 6. The master disk of claim 1, wherein the mastergroove bottoms include sharp corners.
 7. The master disk of claim 1,wherein the master grooves include a groove depth which is approximatethe thickness of the photosensitive material.
 8. The master disk ofclaim 1, wherein the master grooves includes a groove depth which isgreater than 50 nanometers.
 9. The master disk of claim 1, wherein thetrack pitch is less than 425 nanometers, the width of the master groovebottom is greater than 100 nanometers.
 10. The master disk of claim 9,wherein the width of the master groove bottom is greater than 250nanometers.
 11. The master disk of claim 9, wherein the groove depth isgreater than 50 nanometers.
 12. A disk made from a replication processwhich includes a master disk having a data layer formed over a mastersubstrate, the disk comprising: a replica substrate having a first majorsurface and a second major surface, the first major surface including asurface relief pattern in the form of a track pattern defined byadjacent lands and grooves, the track pattern having a track pitch lessthan 425 nanometers, wherein the grooves extend down into the replicasubstrate, the grooves including a groove bottom and the lands includinga land top, wherein the land top is flat.
 13. The disk of claim 12,wherein the land top has a width greater than 35% of track pitch. 14.The disk of claim 12, wherein the groove depth is greater than 50nanometers.
 15. The disk of claim 14, wherein the land width is greaterthan 100 nanometers.
 16. The disk of claim 12, wherein the land top issmooth.
 17. The disk of claim 13, further wherein the land top has sharpedges.
 18. The disk of claim 12, wherein the land tops are level witheach other, such that the flatness of first major surface of the replicadisk is defined by master substrate flatness.
 19. The disk of claim 12,wherein the land tops are level and at the same elevation relative tothe second major surface.
 20. A stamper comprising: a stamper substratehaving a first major surface and second major surface, the first majorsurface including a surface relief pattern in the form of a trackpattern defined by adjacent stamper lands and stamper grooves, whereinthe grooves extend down into the stamper substrate, the stamper groovesincluding a stamper groove bottom and the stamper lands including astamper land top, wherein the stamper groove bottom is wider than thestamper land top.
 21. The stamper of claim 20, wherein the stampergroove bottom is generally flat.
 22. The stamper of claim 20, whereinthe master groove bottoms are flat relative to the master land tops. 23.The stamper of claim 20, wherein the master groove bottoms are levelwith each other.
 24. The stamper of claim 20, wherein the master groovebottoms are wide and flat relative to the master land tops.
 25. Thestamper of claim 20, wherein the master groove bottoms include sharpcorners.
 26. The stamper of claim 20, wherein the master groovesincludes a groove depth which is greater than 50 nanometers.
 27. Thestamper of claim 20, wherein the track pitch is less than 425nanometers, the width of the master groove bottom is greater than 100nanometers.
 28. The stamper of claim 27, wherein the width of the mastergroove bottom is greater than 250 nanometers.
 29. The stamper of claim27, wherein the groove depth is greater than 50 nanometers.